386 Weismanris Theories — 



The position which the minds of men interested in the 

 study of Uving things has thus taken up in our own time, is 

 more or less a return to that mental attitude which marked 

 the earliest days of scientific investigation whereof we have 

 any knowledge. A very large part of Aristotle's biological 

 treatises were directed to this subject, and wonderful indeed 

 are those five books, when studied in the light of our most 

 modern theories. Not of course that such questions were 

 not debated at a yet earlier period. Indeed, a passage in the 

 second chapter of his second book shows that certain very 

 modern theories were rife amongst his predecessors. These he 

 refuted as he refuted Ionian materialism, and his influence 

 for centuries preserved the world from errors of this kind. 

 Owing to this, certain rational ideas about development were 

 retained throughout the Middle Ages — ideas from which the 

 microscopists of the last century went strangely astray. 



Every one is now familiar with the word ' Evolution,' but 

 during the controversies of the seventeenth and eighteenth 

 centuries it was employed in a very different sense from that 

 in which we now use it. The theory then in fashion was 

 that of ' preformation,' according to which the embryo was a 

 perfect miniature of the adult, its development being a mere 

 process of growth, and the unfolding of what already actually 

 existed. Such were the views of Swammerdam, YaUisneri, 

 Boerhaave, Malpighi, and other celebrated observers. But the 

 same arguments which led to such a belief as regards the 

 individual, logically compelled its supporters to maintain 

 that all the individuals destined to arise in the course of 

 ages also existed * preformed in miniature ' — such preformed 

 germs existing one within the other in ever-diminishing 

 proportions. This was the celebrated theory of 'emboite- 

 ment ' which, for speculative reasons, received the patronage 

 of Leibnitz and Malebranche. 



On the other side, our own immortal Harvey (1615) 



